design of the material system and to estimate the effect of how the materials are put together on the performance, economy, and reliability of the resulting component. A more precise understanding of the manufacturing, processing, and component design steps will greatly accelerate the acceptance of these advanced materials. New horizons for properties and performance, for example, in smart and intelligent materials, actuators, sensors, high-temperature organic materials, and multicomponent hybrid systems, will involve the potential of introducing a new age of economic success and technical excellence. It has been estimated that finished-product businesses of greater than $5B annually already exist for the aggregate of polymers, reinforcements, prepregs, tooling machinery, and other ancillary products (McDermott, 1993).

Advanced polymer matrix composites have been used for more than 20 years, for example, on the B-1 bomber and for many top-of-the-line Navy and Air Force jet fighters. For military purposes, the high performance and stealthiness of composites have often outweighed issues of durability and even safety. Building lighter, more maneuverable tanks, trucks, and armored vehicles might be an area for future military growth. However, as the Pentagon's budget shrinks, efforts to transform these materials into civilian uses are under way (Pasztor, 1992). Problems include the need to identify significant nondefense companies that will use advanced composites. For nearly 30 years, it has been suggested that aircraft designers around the world would rapidly utilize these new materials. Unfortunately, those predictions have not been realized, and U.S. plants making polymer matrix composites are now operating at less than 50 percent of capacity. For a number of reasons, there is continued reticence to employ these advanced materials in many areas, particularly in commercial aviation. Costs, processibility, and durability appear to be the major issues. To this point, this area has been considered a technical success but not a financial success. Nevertheless, aircraft in various stages of development have composites as some fraction of their structural weight. For example, 15 percent of the Boeing 777, 6 percent of the MD-11 Trijet, and 15 percent of the MD-12 are estimated to be composites. European aviation firms have begun flight-testing an all-composite tail rotor for a helicopter, and Japanese efforts are under way to develop a military helicopter that has a very high composite content.

It has been predicted that in the future, fiber-reinforced composites (FRCs) will partially replace conventional materials in civil engineering applications. These could include buildings, bridges, sewage and water treatment facilities, marine structures, parking garages, and many other examples of infrastructure components. Composite materials are also expected to help replace conventional materials such as steel and concrete in many future projects. A volume of $3T for fiber-reinforced composites in the rehabilitation of the country's infrastructure has been estimated (Barbero and Gangarao, 1991). The polymer matrix resin composites discussed above have already made inroads in areas such as antenna coverage and water treatment plants. Less expensive fiber-reinforced

The National Academies of Sciences, Engineering, and Medicine 500 Fifth St. N.W. | Washington, D.C. 20001